IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0

=============================================
[ INFO: possible recursive locking detected ]
IPVS: sync thread started: state = BACKUP, mcast_ifn = lo, syncid = 0, id = 0
IPVS: stopping backup sync thread 5290 ...
4.4.130-g12ef385 #27 Not tainted
---------------------------------------------
syz-executor4/5272 is trying to acquire lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82fb0787>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70

but task is already holding lock:
 (rtnl_mutex){+.+.+.}, at: [<ffffffff82fb0787>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(rtnl_mutex);
  lock(rtnl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by syz-executor4/5272:
 #0:  (rtnl_mutex){+.+.+.}, at: [<ffffffff82fb0787>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 #1:  (ipvs->sync_mutex){+.+.+.}, at: [<ffffffff831c04f0>] do_ip_vs_set_ctl+0x8e0/0xb70 net/netfilter/ipvs/ip_vs_ctl.c:2356

stack backtrace:
CPU: 0 PID: 5272 Comm: syz-executor4 Not tainted 4.4.130-g12ef385 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 0000000000000000 05527659f204332f ffff8800ae59f4c0 ffffffff81e0dc6d
 ffffffff8539cdf0 ffffffff8539cdf0 ffffffff8539cdf0 ffff8801ccdb6900
 00000002d47620b5 ffff8800ae59f668 ffffffff8140fb01 ffffffff8574bb80
Call Trace:
 [<ffffffff81e0dc6d>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81e0dc6d>] dump_stack+0xc1/0x124 lib/dump_stack.c:51
 [<ffffffff8140fb01>] print_deadlock_bug kernel/locking/lockdep.c:1752 [inline]
 [<ffffffff8140fb01>] check_deadlock kernel/locking/lockdep.c:1796 [inline]
 [<ffffffff8140fb01>] validate_chain kernel/locking/lockdep.c:2128 [inline]
 [<ffffffff8140fb01>] __lock_acquire.cold.58+0x154/0x58a kernel/locking/lockdep.c:3213
 [<ffffffff8123585e>] lock_acquire+0x15e/0x450 kernel/locking/lockdep.c:3592
 [<ffffffff838b7b6b>] __mutex_lock_common kernel/locking/mutex.c:521 [inline]
 [<ffffffff838b7b6b>] mutex_lock_nested+0xbb/0x850 kernel/locking/mutex.c:621
 [<ffffffff82fb0787>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff833134fc>] ip_mc_drop_socket+0x8c/0x230 net/ipv4/igmp.c:2590
 [<ffffffff832f605b>] inet_release+0x5b/0x1d0 net/ipv4/af_inet.c:421
 [<ffffffff82f18356>] sock_release+0x96/0x1c0 net/socket.c:586
 [<ffffffff831d30e8>] start_sync_thread+0xa18/0x1ed0 net/netfilter/ipvs/ip_vs_sync.c:1923
 [<ffffffff831c0502>] do_ip_vs_set_ctl+0x8f2/0xb70 net/netfilter/ipvs/ip_vs_ctl.c:2357
 [<ffffffff830c4d7d>] compat_nf_sockopt net/netfilter/nf_sockopt.c:145 [inline]
 [<ffffffff830c4d7d>] compat_nf_setsockopt+0x10d/0x130 net/netfilter/nf_sockopt.c:155
 [<ffffffff83224457>] compat_ip_setsockopt+0xa7/0xe0 net/ipv4/ip_sockglue.c:1253
 [<ffffffff832c918a>] compat_udp_setsockopt+0x4a/0x90 net/ipv4/udp.c:2169
 [<ffffffff82f22b84>] compat_sock_common_setsockopt+0xb4/0x150 net/core/sock.c:2670
 [<ffffffff8300971c>] C_SYSC_setsockopt net/compat.c:384 [inline]
 [<ffffffff8300971c>] compat_SyS_setsockopt+0x14c/0x2a0 net/compat.c:367
 [<ffffffff81006d96>] do_syscall_32_irqs_on arch/x86/entry/common.c:392 [inline]
 [<ffffffff81006d96>] do_fast_syscall_32+0x326/0x8b0 arch/x86/entry/common.c:459
 [<ffffffff838c0e6a>] sysenter_flags_fixed+0xd/0x17
IPVS: stopping backup sync thread 5282 ...
IPVS: stopping backup sync thread 5286 ...
IPVS: stopping backup sync thread 5289 ...
IPVS: stopping backup sync thread 5287 ...
IPVS: stopping backup sync thread 5288 ...